Re: Logical replication timeout problem

On Thu, Mar 31, 2022, at 11:27 PM, Amit Kapila wrote:
> This is exactly our initial analysis and we have tried a patch on
> these lines and it has a noticeable overhead. See [1]. Calling this
> for each change or each skipped change can bring noticeable overhead
> that is why we decided to call it after a certain threshold (100) of
> skipped changes. Now, surely as mentioned in my previous reply we can
> make it generic such that instead of calling this (update_progress
> function as in the patch) for skipped cases, we call it always. Will
> that make it better?
That's what I have in mind but using a different approach.

> > The functions CreateInitDecodingContext and CreateDecodingContext receives the
> > update_progress function as a parameter. These functions are called in 2
> > places: (a) streaming replication protocol (CREATE_REPLICATION_SLOT) and (b)
> > SQL logical decoding functions (pg_logical_*_changes). Case (a) uses
> > WalSndUpdateProgress as a progress function. Case (b) does not have one because
> > it is not required -- local decoding/communication. There is no custom update
> > progress routine for each output plugin which leads me to the question:
> > couldn't we encapsulate the update progress call into the callback functions?
> >
>
> Sorry, I don't get your point. What exactly do you mean by this?
> AFAIS, currently we call this output plugin API in pgoutput functions
> only, do you intend to get it invoked from a different place?
It seems I didn't make myself clear. The callbacks I'm referring to the
*_cb_wrapper functions. After every ctx->callbacks.foo_cb() call into a
*_cb_wrapper() function, we have something like:

if (ctx->progress & PGOUTPUT_PROGRESS_FOO)
NewUpdateProgress(ctx, false);

The NewUpdateProgress function would contain a logic similar to the
update_progress() from the proposed patch. (A different function name here just
to avoid confusion.)

The output plugin is responsible to set ctx->progress with the callback
variables (for example, PGOUTPUT_PROGRESS_CHANGE for change_cb()) that we would
like to run NewUpdateProgress.

--
Euler Taveira
EDB https://www.enterprisedb.com/